This invention relates generally to gas chromatography systems and methodology, and more specifically relates to apparatus and techniques used in such environments for regulating oven temperatures.
Gas chromatographic systems commonly include an oven which surrounds the chromatographic column as to maintain a desired operating temperature. In many instances, an operating temperature range of interest occurs at a zone slightly above ambient. Efforts to maintain the system oven temperature in these ranges, have in the past taken the form on the one hand of overly complex and expensive approaches requiring the use of sophisticated and costly components; or on the other hand relatively makeshift and by and large unacceptable techniques have been utilized.
For example, coolants such as liquid nitrogen or carbon dioxide have been employed where it was necessary to produce temperatures below a minimum level established by heat produced by the oven mixing fan and losses through oven insulation from other heated zones. When desired temperatures were below this minimum level, but higher than ambient air temperature, a common but completely makeshift technique has involved manually opening the oven door to create an uncontrolled heat leak. This last approach, while somewhat effective for its purposes, produces unstable and non-repeatable results.
Within recent years, efforts have been undertaken to mechanize the door opening approach so that the results thereof would be more stable and repeatable in nature. The techniques thus far contemplated, however, have involved simple opening and closing of the said oven door in response to temperature sensor determinations, the net result of which is to produce pulsations of cooler ambient air as the latter enters the oven chamber. In consequence, undesirable gradients can occur. Detectors such as those operating on the thermal conductivity principle, are highly sensitive to such gradients, and the end result is a deterioration of signal quality.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a system for controllably opening and closing the oven door in a gas chromatographic system, in such manner that the temperature conditions within the oven may be accurately controlled and rapidly stabilized at a set temperature, without undue oscillations occuring in the said system.